Alexander M. Astachov

Powder diffraction crystal structure analysis using derivative difference minimization : example of the potassium salt of 1-(tetrazol-5-yl)-2-nitroguanidine

The crystal structure of the potassium salt of 1-(tetrazol-5-yl)-2-nitroguanidine [K(C2H3N8O2)] was solved and refined from X-ray powder diffraction data by applying the derivative difference minimization (DDM) method. The compound is of interest as an energetic substance. The structure model was found from a Patterson search. The reflection intensities for the Patterson synthesis were derived from the powder profile by applying a newly developed DDM-based profile decomposition procedure. The use of the DDM method allowed successful location and unconstrained refinement of all the atomic positions, including those of three independent H atoms. The advantages of DDM in terms of the precision and reproducibility of the structural parameters are discussed in comparison to Rietveld refinement results. The failure to refine the H-atom positions by the Rietveld method was attributed to systematic errors associated with the background modelling, which are avoided by DDM.

1,2-dinitroguanidine.

The title compound, CH(3)N(5)O(4), is almost planar, and the conformation is fixed by two intramolecular N-H...O hydrogen bonds. Owing to the delocalization of pi-electron density over the whole molecule, there is through-conjugation, with the C-N, N-N and N-O bond lengths having values intermediate between those typical for the corresponding single and double bonds.

2-nitrimino-1-nitroimidazolidine.

The molecule of the title compound, C(3)H(5)N(5)O(4), has a planar geometry. Due to the presence of a second nitro group, the lengths of the two conjugated C--N bonds are different. Nevertheless, the conjugation of the nitrimine group spreads to the nitramine group. Intermolecular N--H...O bonds connect molecules into dimers in the crystal structure.

5-Nitro-2-nitromethyl-2H-1,2,3,4-tetrazole

The molecule of the title compound, C(2)H(2)N(6)O(4), consists of three planar fragments, namely a tetrazole ring, a nitromethyl group and a nitro group. The nitro group and the tetrazole cycle are arranged in the same plane, but the planar nitromethyl group is located nearly orthogonal to this plane. The molecules are packed in the crystal via van der Waals interactions.

3-Nitro-1-nitromethyl-1H-1,2,4-triazole

The title compound, C(3)H(3)N(5)O(4), consists of three planar fragments twisted in relation to each other, namely a triazole ring, a nitromethylene group and a nitro group. Molecular conformation analysis shows that the first stage of thermal decomposition is a breakage of the H(2)C-NO(2) bond. There are essential conformational differences in the molecule in comparison with semi-empirical calculations.

4-Nitramino-1,2,4-triazole

4-Nitramino-1,2,4-triazole (4-NRTZ), C 2 H 3 N 5 O 2 , consists of two almost planar fragments, namely a triazole ring and nitroimide group, N(NO 2 ); the angle between these two planes is 50.55 (6)°. The nitroimide group is connected to the triazole ring by the longest N-N bond. H atoms are localized near the C3, C5 and N2 atoms in the triazole ring. Analysis of the crystal structure suggests that the first stage of decomposition of 4-NRTZ is a breakage of the N4-N6 bond.

Crystal structure of S,S′-dimethyl-N-nitroimidodithiocarbonate

The molecule of S,S′-dimethyl-N-nitroimidodithiocarbonate has a planar geometry (with the exception of hydrogen atoms of methyl groups), stabilized by the shortened S…O contact. The bond lengths in the >С=N–NO2 nitrimine moiety, in contrast to nitroguanidine derivatives, make it possible to consider the molecular structure of the compound within the traditional valence formula. The crystal structural feature of the compound is a low energy of its crystal lattice.

1-Amino-2-nitraminoethane.

The molecule of title compound, C(2)H(7)N(3)O(2), has a zwitterionic structure. All non-H atoms, apart from the terminal N atom of the NH(3) group, lie in the same plane, with a maximum deviation of 0.056 (1) A for the amine N atom of the nitramine group, whereas the deviation of the terminal N atom of the NH(3) group from the same plane is 1.222 (2) A. Intermolecular hydrogen bonds within the crystal form a three-dimensional network.